A natural hormone, a G2 factor, within the cotyledons of Pisum that promotes cell arrest in G2 in mature root tissue and stationary phase root and shoot meristems has been demonstrated. Experiments are directed towards elucidation of the chemical structure and further characterization of the response of cells in roots and shoots to the G2 factor. This developmental system facilitates a concise example of natural hormonal regulation of the mitotic cycle and cellular differentiation in complex tissues. The molecular structure of the G2 factor will be obtained from samples taken from sequential elution after Dowex and Sephadex LH-20 chromatography. The purity of the eluents from the Sephadex column will be monitored by thin layer chromatography. The molecular structure will be obtained with the use of field desorption mass spectrometry with suitable standards. Specific questions to be answered are: (1) Is the presence or absence of any other tissue related to the G2 factor? (2) What cells in roots are preferentially arrested in G2 by the G2 factor? (3) Can we localize the responsive cells in shoots? (4) Does the G2 factor influence any morphogenetic phenomena in shoots such as (a) leaf initiation rate, (b) growth fraction of the meristem, or (c) the cell cycle kinetics of shoots?